(a) Field
Embodiments relate to a feedback circuit and a power supply device including the same. Particularly, Embodiments relate to a feedback circuit for preventing an output voltage overshoot of a power supply device and a power supply device including the same.
(b) Description of the Related Art
In a system in which a control loop for variation in output voltage is slow, the output voltage may be increased by overvoltage. A power supply device may be controlled so that fluctuation which is generated in an AC line connected to an input terminal is not reflected to the output voltage and current. To this end, a constant voltage and constant current control loop of the power supply device may be used, but response to the control loop may be slower as compared with rapid fluctuation in input voltage and a load.
For example, an overshoot of the output voltage may be generated during a start-up period of the power supply device. When the control loop is relatively slow, an operation of the power supply device for the fluctuation in the output voltage of the power supply device is not rapidly controlled.
In detail, when the power supply device is controlled by a pulse width modulation method, a pulse width modulation controller may control a duty cycle of a power switch according to feedback voltage corresponding to the fluctuation in the output voltage. When the control loop is slow, the feedback voltage does not respond promptly to the increase of the output voltage and particularly, the feedback voltage of the controller keeps in a maximum value while the output voltage increases during the start-up period. Then, an overshoot of the output voltage in an optimal level or more is generated while the feedback voltage keeps in a maximum value and until the feedback voltage is decreased at the optimal level by reacting to the overshoot of the output voltage, the output voltage is maintained by the overvoltage.
The overshoot and the overvoltage of the output voltage damage the load connected to the output terminal and components of the power supply device and excessively increase drain-source voltage of the power switch.
The problems may also occur in the case where the input voltage of the power supply device is rapidly increased or the load is rapidly fluctuated, as well as the start-up period.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.